Line 13x9-inch pan with foil, with ends of foil extending over sides of pan; lightly grease foil.
Microwave butter in large microwaveable bowl on HIGH 45 sec. or until melted.
Add marshmallows; toss to coat. Microwave 1-1/2 min. or until marshmallows are completely melted and mixture is well blended, stirring after 45 sec.
Add cereal; mix well.
Press cereal mixture onto bottom of prepared pan. Cool completely.
Use foil handles to remove cereal mixture from pan; cut into star shapes with large star-shaped cookie cutter. Insert wooden pop stick into side of each star. Decorate with gels and sprinkles.